Purpose: To evaluate acid-etching effects prior to the application of self-etching primer and the effect of different primer application techniques on dentin shear bond strength (SBS). Materials and Methods: Forty human third molar cervical regions were used in this study. The teeth were randomly divided into four groups (n = 10) of different tooth surface conditions: group A: Clearfil Protect Primer applied gently (inactive) + Clearfil Protect Bond; group B: 38% phosphoric acid for 15 s, rinsed 15 s, and dried 15 s + Clearfil Protect Primer applied gently (inactive) + Clearfil Protect Bond; group C: Clearfil Protect Primer applied with agitation by microapplicator brush (active) + Clearfil Protect Bond; group D: 38% phosphoric acid for 15 s, rinsed 15 s, and dried 15 s + Clearfil Protect Primer applied with agitation by microapplicator brush (active) + Clearfil Protect Bond. The SBS test was performed with a universal testing machine at a crosshead speed of 1 mm/min. Data were analyzed with one-way ANOVA and Tukey HSD tests. Results: The mean SBS values (MPa) and standard deviations are as follows: group A: 36.0 ± 8.3; group B: 24.0 ± 3.9; group C: 35.0 ± 3.3; group D: 30.6 ± 6.7. Conclusion: Acid etching decreased the SBS of the self-etching bonding system to dentin. Active primer application increased the SBS only in acid-etched groups.

Keywords: self-etching primer, acid etching, application procedure, shear bond strength